A good rule of thumb is to assume an average of 30 miles per hour (50 km per hour). The roads in Costa Rica are sinuous and patchy, and generally even highways only have two lanes, with little room to pass, if any. All kinds of vehicles ride these roads and some –like the big trucks- can slow the traffic down a lot.
However, just to give you an idea, here’s a list of the approximate times it takes between some of Costa Rica’s most popular destinations:
Alajuela-SJO to Arenal – 3 hrs.
Alajuela-SJO to Mal Pais – 5-6 hrs.
Alajuela-SJO to Manuel Antonio – 3 hrs.
Alajuela SJO to Monteverde – 3 hrs.
Alajuela-SJO to Puerto Viejo, Limon – 5 hrs.
Arenal to Tamarindo – 3.5 hrs.
Liberia to Arenal – 3hrs.
Liberia to Tamarindo – 1 hr.
Monteverde to Samara – 3.5 hrs.